Alterations in glycogen content of mammalian host muscle infected with the parasitic nematode, Trichinella spiralis, and concomitant changes in the total glycogen of T. spiralis, larvae in such muscle is well known (Flury, 1913; Zarzycki, 1956; Becket and Boothroyd, 1961; Karpiak et al., 1963; Stewart, 1976). Preliminary studies in this laboratory have revealed that excysted T. spiralis muscle larvae and larvae encysted within host muscle incorporate significant quantities of 14C-glucose into glycogen during 4-hr incubations in vitro. The objective of the proposed research is to elucidate the molecular interactions between the mouse host and T. spiralis larvae as it involves glycogen metabolism. To accomplish these goals we will investigate alterations in key enzymes involved in the synthesis, breakdown and utilization of glycogen in muscle and liver tissues from Trichinella-infected and control mice as well as in muscle larvae. Changes in tissue levels of cyclic AMP will also be evaluated. The source(s) of glucose involved in the observed increase in trichinous muscle and larval glycogen, and the effects of several host hormones on larval glycogen metabolism will also be investigated. The proposed work will elucidate the molecular integration of glycogen metabolism between host and parasite, as well as uncover some of the basic feedback control mechanisms imposed on parasite metabolsim by the host and on host metabolism by the parasite. This will contribute to a better understanding of how the host muscle is involved in providing a biochemically suitable environment for the muscle larva and will advance our understanding of the molecular integration of the host and the parasite in intracellular parasitism in general.